Looks amazing
. It just oozes class! Enjoyed reading that thorough summary too. Shame about the bit hiss, I've been doing a bit of research on this recently, because sometimes no amount of cleaning that eradicate it.
For anyone wanting to understand further, this below is worth a read. It tries to explain why audio circuits make noise (the hiss). Most of it went over my head though..
http://sound.westhost.com/noise.htm
Great article! Short version for the less technically inclined -
Signal to noise ratio is the important number with noise.
Preamps have the most effect on total noise.
Very good opamps and transistors exist that can cut noise way down - for a price.
Really cheap resistors in the preamp circuit will have an effect on noise. Really high quality resistors can cut out noise in that circuit by 3-10 dB
Discrete op-amps (transistor pairs) in parallel can cut noise down even further than integrated ones, by up to almost 10dB if well executed.
A lot of people try to goose spec'd noise down as low as possible through vague reporting in the specs.
Rules of thumb - On digital systems, you should add 10 dB to the stated S/N ratio to get analogue equivalent.
- When only input noise is specified (i.e. -120 dB), you must add amp gain (about 40 for 100 watt amps) to get S/N (in that case, -80 dB)
- If the amp gives a "noise figure" with awkward units, it is possible to convert to dB, but you probably won't like how bad the figure is. and don't forget to add those other effects
- Rebuilding/restoring vintage units with tight tolerance, high quality components can make them even better